Asymmetric acidification of a membrane-electrode assembly

Abstract

In one embodiment, a method of making an MEA for a fuel cell comprises arranging a cathodic structure on a first surface of a PEM, and arranging an anodic structure on a second surface of the PEM, opposite the first surface, the anodic structure containing more PA per unit volume than the cathodic structure. The method further comprises pressing the cathodic and anodic structures to the PEM to form the MEA.

1 . A method of making a membrane-electrode assembly for a fuel cell, the method comprising:
 arranging a cathodic structure on a first surface of a polymer-electrolyte membrane;   arranging an anodic structure on a second surface of the polymer-electrolyte membrane, opposite the first surface, the anodic structure containing more phosphoric acid per unit volume than the cathodic structure;   pressing the cathodic and anodic structures to the polymer-electrolyte membrane to form the membrane-electrode assembly.   
     
     
         2 . The method of  claim 1 , wherein the cathodic structure does not include phosphoric acid. 
     
     
         3 . The method of  claim 1 , further comprising adding phosphoric acid to one or more components of the anodic structure. 
     
     
         4 . The method of  claim 1 , further comprising adding phosphoric acid to the polymer-electrolyte membrane. 
     
     
         5 . The method of  claim 1 , further comprising applying the cathodic structure to a cathodic gas-diffusion layer, and applying the anodic structure to an anodic gas-diffusion layer. 
     
     
         6 . The method of  claim 1 , wherein applying the cathodic and anodic structures to their respective gas-diffusion layers comprises applying from a suspension of particles and dissolved solids in a solvent. 
     
     
         7 . The method of  claim 6 , wherein the suspension from which the anodic structure is applied includes more phosphoric acid per unit volume than the suspension from which the cathodic structure is applied. 
     
     
         8 . The method of  claim 6 , further comprising applying phosphoric acid to the anodic structure from a solution different than the suspension from which the anodic structure is applied. 
     
     
         9 . A fuel cell comprising:
 a membrane-electrode assembly including a polymer-electrolyte membrane having a cathodic structure arranged on a first surface and an anodic structure arranged on a second surface opposite the first surface, the anodic structure containing more phosphoric acid per unit volume than the cathodic structure;   a cathodic bipolar plate disposed in face-sharing contact with the cathodic structure;   an anodic bipolar plate disposed in face-sharing contact with the anodic structure.   
     
     
         10 . The fuel cell of  claim 9 , wherein the polymer-electrolyte membrane comprises a polybenzimidazole. 
     
     
         11 . The fuel cell of  claim 9 , wherein the cathodic structure includes a cathodic catalyst layer arranged in direct contact with the first surface and a cathodic microporous layer arranged over the cathodic catalyst layer, opposite the first surface, and wherein the anodic structure includes an anodic catalyst layer arranged in direct contact with the second surface and an anodic microporous layer arranged below the anodic catalyst layer, opposite the second surface. 
     
     
         12 . The fuel cell of  claim 11 , wherein the cathodic structure further includes a cathodic gas-diffusion layer arranged over the cathodic microporous layer, and wherein the anodic structure includes an anodic gas-diffusion layer arranged below the anodic microporous layer. 
     
     
         13 . The fuel cell of  claim 12 , wherein the anodic microporous layer is thicker than the cathodic microporous layer, but the anodic catalyst layer is not thicker than the cathodic catalyst layer. 
     
     
         14 . The fuel cell of  claim 9 , wherein the anodic structure is thicker than the cathodic structure. 
     
     
         15 . The fuel cell of  claim 9 , wherein the anodic structure includes more silicon carbide per unit volume than the cathodic structure. 
     
     
         16 . The fuel cell of  claim 9 , wherein the amount of phosphoric acid included in the polymer-electrolyte membrane and in the anodic structure exceeds fifteen milligrams per square centimeter of the membrane. 
     
     
         17 . A method of assembling a fuel cell, comprising:
 installing between two bipolar plates of the fuel cell a membrane-electrode assembly including a polymer-electrolyte membrane having a cathodic structure arranged on a first surface and an anodic structure arranged on a second surface opposite the first surface, the anodic structure containing more phosphoric acid per unit volume than the cathodic structure; and   applying force to the bipolar plates to seal the bipolar plates to the membrane-electrode assembly without first adding additional phosphoric acid to the cathodic structure.   
     
     
         18 . The method of  claim 17 , further comprising supplying air and fuel to the fuel cell while drawing current from the fuel cell, thereby causing some phosphoric acid retained in the anodic structure to diffuse to the cathodic structure. 
     
     
         19 . The method of  claim 18 , wherein the air and fuel are supplied to the fuel cell and the current is drawn from the fuel cell during a conditioning phase wherein an operating voltage of the fuel cell increases. 
     
     
         20 . The method of  claim 18 , wherein supplying air and fuel to the fuel cell comprises supplying fuel enriched in phosphoric acid vapor.